Marking systems that transport paper or other media are well known in the art. These marking systems include electrostatic marking systems, non-electrostatic marking systems, printers or any other marking system where paper or other flexible media or receiving sheets are transported internally to an output device, such as a finisher and compiler. Many machines are used for collecting or gathering printed sheets so that they may be formed into books, pamphlets, forms, sales literature, instruction books and manuals and the like.
The finisher and compiler are located at a site in these marking systems after the receiving sheets (paper) have been marked. A finisher is generally defined as an output device that has various post printer functions or options such as hole punching, corner stapling, edge stapling, sheet and set stacking, letter or tri-folding, Z-Folding, Bi-folding, signature booklet making, set binding (including thermal, tape and perfect binding), trimming, post process sheet insertion, saddle stitching and others.
The compiler often employs a compiling wall or tray where frictional drive elements hereinafter called elastomer paddle wheels or “paddle wheels” (PW) or scuffers are used to drive sheets (paper) against the compiling wall for registration of the staple or bind edge of a set. If desirable, belts or scuffer wheels may be used, etc. instead of paddle wheels. The force of these frictional drive elements on the sheet is critical and, must be controlled within narrow limits. In the case of Deflection Loaded technologies, such as Paddle Wheels, the compiler element drive force has been found to be dependent on many factors including the type or thickness of the paper used. In many such finisher compiling systems, the compiler drive element is periodically indexed or adjusted to attempt to compensate for stack misalignment or build up. Sheet counting is frequently used as a criteria to index the Compiler Drive element shaft, but it does not successfully comprehend curl build up or variations in paper weight/thickness.
The compiling capacity and bind edge sheet registration can be compromised with moderate to severe misalignment of the sheets. Excessive misalignment can cause poor set registration and possibly paper jams or sheet damage.
As discussed above in [003], finisher compiling systems often employ frictional drive elements such as foam scuffer wheels or elastometric paddle wheels to drive the individual sheets square (deskewed) and against the registration edge. With such compliant drive elements, the normal force on the paper and, thus, the drive force, will differ as the paper weight or thickness changes.
What can occur is that if there is too little drive force, the sheets will not be properly registered or deskewed. Too much drive force and the top sheets will buckle causing poor set registration and possibly sheet damage or a jam or limiting set size (thickness) compiled.
As noted, differences in media weight and curl will have significant, if not, dramatic effects on the net available drive force and thus upon the final sheet alignment condition. Additionally, any drag forces acting on the sheet may further reduce the net drive force and thus affect sheet alignment.
A rapid increase in on-demand service to provide large-volume small-scale printing of brochures, etc. by use of color/black and white multifunction machines has been exhibited. Even ordinary offices are stepping up their efforts at in-house production of conference paper, simple booklets, manuals and other materials by establishing service departments for intensively processing prints in large quantities. Such customers require post-processing functions, such as high-speed/high-precision punching, stapling and paper folding work with simultaneous print output and realization of high-speed/high-quality print output with a high degree of reliability.
“Drive elements or frictional drive elements” as used in this disclosure and claims include any suitable drive element. Also, any number of scuffers or paddle wheels usually elastomer and any suitable number of sensors may be used. The size, type, and number of paddle wheels and blade depend upon many variations in the paper used, such as size of paper, weight of paper, coated or non-coated paper, paper for color prints, paper for monochrome prints, etc. and the specific compiler tray geometry. Also, curl suppressors can be desirably used together with the paddle wheels to improve paper registration. The desired or ideal drive force of the paddle wheels will, of course, vary as the conditions, paper and paper size and other variables change or exist; this ideal drive force can be easily established through simple tests and then fixed in the controller used.
In many finisher compilers, a scuffer mechanism is employed to frictionally drive sheets up to a fixed registration wall. Sheet lead edges are aligned both along the process direction, as well as deskewed as they are forced into contact with the wall. As an example, a High Capability Stacker utilizes three scuffer belts that are intermittently driven so as to draw each incoming sheet across the stack and against the registration wall. The frictional drive elements or scuffer imparts a drive force to the top of each sheet through a predetermined normal force and a controlled friction coefficient. There is a very significant tradeoff involved in determining the optimum drive force. A large heavyweight sheet may offer a high resistance to motion and thus may slip within the scuffer. The scuffer must remain driving for sufficient time so that the sheet ends up properly registered. By contrast, a small lightweight sheet may offer little resistance to motion and have no slip. This sheet will reach the registration wall much sooner and will then be forced to slip and/or buckle until the scuffer is turned off. It would be advantageous if a schedule of different scuffer motion profiles were available for different media types, but drag force variations due to electrostatic forces, curl, etc. make this impractical.